Delta Air Lines , the world's biggest airline, boosted its operating margin forecast for the third quarter, citing lower fuel costs, and said other financial measures were trending in line with or better than year-earlier and second-quarter levels.

In a federal filing on Monday, the company said it expects operating margin of 3 percent to 4 percent for the third quarter, and breakeven operating margin for the full year.

On July 22, Delta projected third-quarter operating margin of 1 percent to 3 percent.

The higher forecast is a positive, said Basili Alukos, a Morningstar analyst.

All the airlines have improved, mostly from a cost perspective, just because fuel has fallen significantly and they've cut capacity, Alukos said.

Helane Becker, an analyst with Jesup & Lamont Securities, raised her third-quarter earnings estimate for Delta from a loss of 30 cents a share to a profit of 5 cents a share and reiterated her buy rating on the stock.

She said Delta's projected load factor performance suggested bookings are strengthening. We believe that business traffic is starting to return to the market, Becker said in a research note.

Delta said load factors -- the percentage of seats filled on planes -- were expected to be about 82 percent for September and October, in line with or slightly above year-earlier levels.

Still, Alukos said he was surprised that Delta indicated its unrestricted liquidity was continuing to fall. Delta projected that measure would stand at $4.6 billion for the full year, compared with $5 billion for the third quarter.

The airline said it expects a consolidated fuel price, net of hedges, of $2.14 per gallon for the third quarter, $2.05 for the fourth quarter, and $2.13 for the full year. In July it forecast $2.17 for the third quarter.

Delta said revenue per available seat mile, an important measure, would show a smaller decline in the third quarter than in the second quarter.

Atlanta-based Delta and other carriers have been cutting capacity and jobs to lower costs as the recession hurts air travel.

Delta said it expects system capacity to be down 4 percent to 5 percent for the third quarter from a year earlier.

For the legacy carriers, the only way improvement is going to come is when they see top-line growth, Alukos said.

Delta shares were up 17 cents at $8.23 in morning New York Stock Exchange trading. Other U.S. carriers were also higher.

(Reporting by Karen Jacobs; editing by John Wallace)